Mount Sinai Researchers Identify Dysregulation of RNA Editing as a Primary Driver of Altered Fetal Brain Development in Down Syndrome

Scientists identify that an extra copy of the ADARB1 gene in Down syndrome causes premature RNA editing, disrupting early fetal brain circuit formation.

By: AXL Media

Published: Mar 31, 2026, 6:07 AM EDT

Source: Information for this report was sourced from The Mount Sinai Hospital / Mount Sinai School of Medicine.

Uncovering the Molecular Impact of Trisomy 21

Down syndrome, or trisomy 21, is defined by the presence of a third copy of chromosome 21. While the genetic cause has been known for decades, the specific biological mechanisms by which this extra material reshapes early brain formation have remained elusive. Researchers from Mount Sinai and the Lieber Institute for Brain Development have now pinpointed a specific gene—ADARB1—located on the tripled chromosome that appears to play a central role. The study finds that the resulting "gene dosage imbalance" leads to an overproduction of the ADARB1 enzyme, which in turn causes widespread errors in how genetic messages are edited before being turned into proteins.

The Role of ADARB1 in Premature RNA Recoding

RNA editing is a natural, essential process that fine-tunes protein function, particularly in the brain. However, in the brains of fetuses with Down syndrome, this process occurs too early and too extensively. The research team analyzed brain tissue from the prefrontal cortex and hippocampus—regions vital for learning and memory—collected between 13 and 22 weeks of gestation. They found that excess ADARB1 drives "RNA recoding," a process where a single change in the RNA sequence alters the amino acid composition of the final protein. This premature maturation of proteins happens at a critical window when the brain's "wiring" is just beginning to take shape.

Disrupting the Balance of Brain Signaling

The study identified specific disruptions in key glutamate and GABA-receptor genes, including GRIA2, GRIA3, GRIK2, and GABRA3. These receptors are responsible for regulating excitatory and inhibitory signals between neurons. By recoding these proteins too early, the ADARB1 enzyme alters how brain cells communicate before neural circuits are even fully established. This imbalance between "on" and "off" signals is predicted to have lasting effects on cognitive development and brain connectivity, providing a molecular explanation for the neurological characteristics associated with Down syndrome.